The most immersive virtual reality and augmented reality experiences have six degrees of freedom, parallax, and view-dependent lighting. Generating viewpoint video for the user directly from the captured video data can be computationally intensive, resulting in a viewing experience with lag that detracts from the immersive character of the experience. Many dedicated virtual reality headsets have sensors that are capable of sensing the position and orientation of the viewer's head, with three dimensions for each, for a total of six degrees of freedom (6DOF).
However, use of mobile phones for virtual reality is becoming increasingly popular. Many mobile phones are designed to detect orientation, but lack the hardware to detect position with any accuracy. Accordingly, the viewer may feel constrained, as the system may be incapable of responding to changes in the position of his or her head.